(1) may 18, 2010, marked 30 years since the eruption of mt. st. helens in washington state. (2) the volcano had been assumed to be rather dormant, so the magnitude of the event was surprising, even to volcanologists. (3) predicting an eruption is quite challenging, but there are a number of warning signs. (4) if a volcano is getting close to erupting, the gases it emits will change, as will its pattern of earthquakes. (5) volcanoes may even begin to change their shape as material is moving within them. (6) this happened with mt. st. helens, as it began to bulge visibly from one side.
(7) scientists have a hard time forecasting exactly when a volcano will erupt. (8) often, eruptions aren't accurately predicted because scientists don't have the measurements they need. (9) however, in mexico in 1993, a high level of sulfur dioxide—one of the volcanic gases—was detected around a volcano near mexico city. (10) warnings were issued to the mexican government that an eruption may be looming. (11) it wasn't until many months later that the volcano finally did erupt. (12) scientists say what they most need in order to more successfully predict eruptions is simply more eruptions! (13) that would allow them to test their theories on the real thing.
what does the author use to illustrate how warning signs can predict an eruption?
a.
examples of measurements taken around mt. st. helens before it went off
b.
statistics about increased earthquake activity around mt. st. helens in 1980
c.
a description of how difficult it is to predict the exact time of a volcanic eruption
d.
the example of gases detected around a mexican volcano before it erupted